Failed despots and the equitable distribution of fitness in a subsidized species

Territorial species are often predicted to adhere to an ideal despotic
distribution and under-match local food resources, meaning that
individuals in high-quality habitat achieve higher fitness than those in
low-quality habitat. However, conditions such as high density, territory
compression, and frequent territorial disputes in high-quality habitat are
expected to cause habitat quality to decline as population density
increases and, instead, promote resource matching. We studied a highly
human-subsidized and under-matched population of Steller’s jays
(Cyanocitta stelleri) to determine how under-matching is maintained
despite high densities, compressed territories, and frequent agonistic
behaviors, which should promote resource matching. We examined the
distribution of fitness among individuals in high-quality, subsidized
habitat, by categorizing jays into dominance classes and characterizing
individual consumption of human food, body condition, fecundity, and core
area size and spatial distribution. Individuals of all dominance classes
consumed similar amounts of human food and had similar body condition and
fecundity. However, the most dominant individuals maintained smaller core
areas that had greater overlap with subsidized habitat than those of
subordinates. Thus, we found that 1) jays attain high densities in
subsidized areas because dominant individuals do not exclude subordinates
from human food subsidies and 2) jay densities do not reach the level
necessary to facilitate resource matching because dominant individuals
monopolize space in subsidized areas. Our results suggest that
human-modified landscapes may decouple dominance from fitness and that
incomplete exclusion of subordinates may be a common mechanism
underpinning high densities and creating source populations of
synanthropic species in subsidized environments.